Caption: Caricature of the Hungarian-German physicist Philipp Lenard (1862-1947). Lenard's early work included studies of phosphorescence and luminescence, but it was his study of cathode rays that lead to him being awarded the 1905 Nobel Prize in Physics. He proved that cathode rays are created when light strikes a metal surface, a phenomenon that later became known as the photoelectric effect and that was explained by Einstein in 1921. He also showed that cathode rays were streams of negatively charged particles that were smaller than molecules in the air. These particles were later named electrons.